Ok; looks like ensuring the cipher set as per recommendation has helped us.

Ensure the list of ciphers is a modern list such as:
`ECDHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES128-SHA256:AES128-SHA:AES256-GCM-SHA384:AES256-SHA256:AES256-SHA:ECDHE-RSA-DES-CBC3-SHA:DES-CBC3-SHA’

"Not having these guidelines implemented will not prevent your webhook from functioning, but are highly reccomended by the Twitter Information Security team"
But in the newly spun environment, twitter failed to register webhook, though these are only recommended not-necessary.